This invention relates to cryocoolers, and to cryoprobes for use in cryosurgery.
Cryosurgical probes are used to treat a variety of diseases. The cryosurgical probes quickly freeze diseased body tissue, causing the tissue to die after which it will be absorbed by the body or expelled by the body or sloughed off. Cryothermal treatment is currently used to treat prostate cancer and benign prostate disease, breast tumors and breast cancer, liver tumors and cancer, glaucoma and other eye diseases. Cryosurgery is also proposed for the treatment of a number of other diseases.
The use of cryosurgical probes for cryoablation of prostate is described in Onik, Ultrasound-Guided Cryosurgery, Scientific American at 62 (January 1996) and Onik, Cohen, et al., Transrectal Ultrasound-Guided Percutaneous Radial Cryosurgical Ablation Of The Prostate, 72 Cancer 1291 (1993). In this procedure, generally referred to as cryoablation of the prostate, several cryosurgical probes are inserted through the skin in the perineal area (between the scrotum and the anus) which provides the easiest access to the prostate. The probes are pushed into the prostate gland through previously place cannulas. Placement of the probes within the prostate gland is visualized with an ultrasound imaging probe placed in the rectum. The probes are quickly cooled to temperatures typically below xe2x88x92120 C. The prostate tissue is killed by the freezing, and any tumor or cancer within the prostate is also killed. The body will absorb some of the dead tissue over a period of several weeks. Other necrosed tissue may slough off through the urethra. The urethra, bladder neck sphincter and external sphincter are protected from freezing by a warming catheter placed in the urethra and continuously flushed with warm saline to keep the urethra from freezing.
Rapid re-warming of cryosurgical probes is desired. cryosurgical probes are warmed to promote rapid thawing of the prostate, and upon thawing the prostate is frozen once again in a second cooling cycle. The probes cannot be removed from frozen tissue because the frozen tissue adheres to the probe. Forcible removal of a probe which is frozen to surrounding body tissue leads to extensive trauma. Thus many cryosurgical probes provide mechanisms for warming the cryosurgical probe with gas flow, condensation, electrical heating, etc.
A variety of cryosurgical instruments, variously referred to as cryoprobes, cryosurgical ablation devices, and cryostats and cryocoolers, have been available for cryosurgery. The preferred device uses Joule-Thomson cooling in devices known as Joule-Thomson cryostats. These devices take advantage of the fact that most gases, when rapidly expanded, become extremely cold. In these devices, a high pressure gas such as argon or nitrogen is expanded through a nozzle inside a small cylindrical sheath made of steel, and the Joule-Thomson expansion cools the steel sheath to sub-freezing cryogenic temperature every rapidly.
An exemplary device is illustrated in Sollami, Cryogenic Surgical Instrument, U.S. Pat. No. 3,800,552 (Apr. 2, 1974). Sollami shows a basic Joule-Thomson probe with a sheath made of metal, a fin-tube helical gas supply line leading into a Joule Thomson nozzle which directs expanding gas into the probe. Expanded gas is exhausted over the fin-tube helical gas supply line, and pre-cools incoming high pressure gas. For this reason, the coiled supply line is referred to as a heat exchanger, and is beneficial because, by pre-cooling incoming gas, it allows the probe to obtain lower temperatures.
Ben-Zion, Fast Changing Heating and Cooling Device and Method, U.S. Pat. No. 5,522,870 (Jun. 4, 1996) applies the general concepts of Joule-Thomson devices to a device which is used first to freeze tissue and then to thaw the tissue with a heating cycle. Nitrogen is supplied to a Joule-Thomson nozzle for the cooling cycle, and helium is supplied to the same Joule-Thomson nozzle for the warming cycle. Preheating of the helium is presented as an essential part of the invention, necessary to provide warming to a sufficiently high temperature.
A Joule-Thomson cryostat for use as a gas tester is illustrated in Glinka, System for a Cooler and Gas Purity Tester, U.S. Pat. No. 5,388,415 (Feb. 14, 1995). Glinka also discloses use of the by-pass from the Joule-Thomson Nozzle to allow for cleaning the supply line, and also mentions that the high flow of gas in the by-pass mode will warm the probe. This is referred to as mass flow warming, because the warming effect is accomplished purely by conduction and convection of heat to the fluid mass flowing through the probe.
Various cryocoolers use mass flow warming, flushed backwards through the probe, to warm the probe after a cooling cycle. Lamb, Refrigerated Surgical Probe, U.S. Pat. No. 3,913,581 (Aug. 27, 1968) is one such probe, and includes a supply line for high pressure gas to a Joule-Thomson expansion nozzle and a second supply line for the same gas to be supplied without passing through a Joule-Thomson nozzle, thus warming the catheter with mass flow. Longsworth, Cryoprobe, U.S. Pat. No. 5,452,582 (Sep. 26, 1995) discloses a cryoprobe which uses the typical fin-tube helical coil heat exchanger in the high pressure gas supply line to the Joule-Thomson nozzle. The Longsworth cryoprobe has a second inlet in the probe for a warming fluid, and accomplishes warming with mass flow of gas supplied at about 100 psi. The heat exchanger, capillary tube and second inlet tube appear to be identical to the cryostats previously sold by Carleton Technologies, Inc. of Orchard Park, N.Y.
Each of the above mentioned cryosurgical probes builds upon prior art which clearly establishes the use of Joule-Thomson cryocoolers, heat exchangers, thermocouples, and other elements of cryocoolers. Walker, Miniature Refrigerators for Cryogenic Sensor and Cold Electronics (1989) (Chapter 2) and Walker and gingham, Low Capacity Cryogenic Refrigeration, pp. 67 et seq. (1994) show the basic construction of Joule-Thomson cryocoolers including all of these elements. The Giaque-Hampson heat exchanger, characterized by coiled finned-tube, transverse flow recuperative heat exchanger is typical of cryocoolers. The open mandrel around which the finned tube coil is placed is also typical of cryocoolers.
Cryosurgical probes may be used, as mentioned above, to treat diseases of the prostate, liver, and breast, and they have gynecological applications as well. The cryosurgical probes form iceballs which freeze disease tissue. Each application has a preferred shape of iceball, which, if capable of production, would allow cryoablation of the diseases tissue without undue destruction of surrounding healthy tissue. For example, prostate cryoablation optimally destroys the lobes of the prostate, while leaving the surrounding neurovascular bundles, bladder neck sphincter and external sphincter undamaged. The prostate is wider at the base and narrow at the apex. A pear or fig shaped ice ball is best for this application. Breast tumors tend to be small and spherical, and spherical iceballs will be optimal to destroy the tumors without destroying surrounding breast tissue. Liver tumors may be larger and of a variety of shapes, including spherical, olive shaped, hot dog shaped or irregularly shaped, and may require more elongated iceballs, larger iceballs, and iceballs of various shapes.
The heat exchanger comprises a Giaque-Hampson heat exchanger with finned tube gas supply line coiled around a mandrel. After expansion in the tip of the cryoprobe, the gas flows over the coils and exhausts out the proximal end of the probe. The flow of exhaust gas over the heat exchanger coils is controlled by placement of a flow directing sheath placed in different longitudinal areas of the heat exchanger. To create spherical iceballs, the thermal barrier is placed over the entire length of the heat exchanger coil. To create pear shaped iceballs, the flow directing sheath is place over the proximal portion of the coil, but not over the distal portion of the coil. For an elongate cylindrical iceball, which we call hot dog shaped, the flow directing sheath is placed over the proximal end of the heat exchanger coil, but not over the distal end of the coil, and the nozzle is placed proximally from the cryoprobe tip. Alternative embodiments include variation of the length of the straight supply tube extending distally from the helical coil heat exchanger, and variation of the distance of the Joule-Thomson nozzle from the distal tip of the probe.
These shapes are desired for the several shapes of tissues that are subject to cryosurgical treatment. The olive-shaped and pear-shaped iceballs are useful for prostate treatment, as they permit creation of the optimal iceball within the prostate. The spherical iceball is desired for treatment of breast tumors, which tend to be spherical. The oblong iceball is desired for treatment of liver tumors, which tend to be oblong. Of course, the correspondence of the shapes to the anatomical site is not a hard and fast rule, and each shape of iceball will be useful in any area of the body wherein a tumor or other condition indicates use of a particular shape.
Parallel finned tubes are used in one embodiment to create a dual helix design. In this embodiment, two parallel gas supply lines are used, and they are wound in parallel around the mandrel. The nozzles tips may be located equidistant from the tip of the probe for a spherical iceball, and they may be offset, with one nozzle placed distally of the other to create an oblong iceball. Both of the dual coils can be used to supply high pressure gas which cools upon expansion (nitrogen, argon, NO2, CO2, etc.), so that both coils are used for cooling. One coil can be used for cooling gas while the other coil is used for the supply of a high pressure gas which heats upon expansion (hydrogen, helium, and neon).
Separate cooling and heating Joule-Thomson nozzles are used in an embodiment wherein the heating gas is supplied through the mandrel. In this embodiment, the heating gas supply is not subject to heat exchange with the exhausting heating gas to create a higher initial heating rate. To permit complete control of both heating and cooling, the several cryoprobes are supplied with gas through a dual manifold which allows for independently warming each probe. This allows removal of individual probes in case the doctor performing the cryosurgery decides that a cryoprobe must be moved after it has formed an iceball. It also allows protective warming for nearby anatomical structures.